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RADIO CONTROL BY BOB YOUNG Multi-channel radio control transmitter; Pt.8 This month we will deal with the more complex programming functions which can be provided in this very advanced R/C transmitter. But first, let’s get this month’s grizzles, whinges and additions out of the way. In Pt.6 (July, 1996), which dealt with the construction of the transmitter case, Fig.2 showed the wiring arrangements for the various control elements. In this drawing set, mention is made of the connecting cable for these functions being a blue/white/ blue 3-core ribbon cable. As these leads are intended for reversing, the blue/white/ blue was to indicate that polarity was not important on these connectors. The b/w/b also matched the transmitter interior which is all in blue and white and it added to the internal appearance. The cable was ordered weeks before that article was written and the order clearly stated blue/white/blue. Months passed and still no cable. The July issue came out, still no cable. Finally, the big day arrived. The delivery docket stated b/w/b, the invoice stated b/w/b but it appears the production people decided that red/white/blue would look much better. As I was desperate for cable by this time I had no alternative but to use the r/w/b ribbon and to my amazement, the production people were absolutely correct. The finished transmitter did look much better, especially since I had increased the cable length after looking at the July issue photos. The leads now run neatly around the sides of the case. From now on, all leads will be red/white/blue as dictated by the cable manufacturers. This has one advantage in that it removes the need to paint a dot on one side of the connector (recommended in the July issue), as it is now very easy to determine visually if the lead is normal or reversed. All jokes aside, this business of quality control is driving me nearly insane. Almost without exception, every major component has been returned due to lack of quality or correctness. My heart is in my mouth every time I open a new batch of components. From powder coating to pots, I have sent back more components than I have accepted. Under these conditions, delivery promises mean nothing, and even now I am still struggling to get the project running smoothly with regards to deliveries. However, I digress. The wiring in those July photos looked totally disorganised. By increasing the lead length, it is now possible to run the leads right around the outside of the case (see photo). This was mentioned in the July issue but not highlighted. The lengths shown in Fig.2 of the July issue were the corrected, longer values. The addition of the frequency interlock key, as described in the text, eliminates the possibility of two transmitters operating on the same channel. 82  Silicon Chip Fig.1: the frequency interlock key, developed by the Author, cuts off the power to the transmitter while it is plugged into the charging socket. When the transmitter is in use, the key is removed and hangs on a key board in the club. Another nice touch added to the kits is the inclusion of self-adhesive cable clamps which stick to the case sides and secure all the cables neatly. These are made out of the large headed split-pin type paper clips, available at any stationers. The legs are clipped in length and covered in heatshrink and the heads stuck to the case side with double-sided foam tape. They sit flat against the wall, can hold a large number of cables and are dead easy to open and close, in order to add and remove cables; in other words, the ideal cable clamp. Also, since the July issue, I have found a source of components for crimp connectors which allows me to crimp my own leads. These feature a housing similar in size to the Futaba servo connector housing but less the polarising flange. These are fitted with high contact pressure, gold-plated pins. All kits will henceforth use these connectors which will be pre-crimped. These connectors are of a higher quality and are less fiddly to assemble than the original solder connectors. They also have one large flat face which is ideal for a self-adhesive numbering label. A sheet of self-adhesive numbers is now included in all kits as an aid in identifying the leads. The following list gives the lead numbers in production transmitters: The view inside the case from the rear. The operating channel is set by the plug-in crystal near the centre top of the photo. The interconnecting wiring is now laid around the perimeter of the case for a much neater appearance. 1. Throttle pot 2. Aileron pot 3. Elevator pot 4. Rudder pot 5. Switch 1 (outside left) 6. Aux 1 pot (left) 7. Switch 2 (inside left) 8. Switch 3 (inside right) 9. Aux 2. Pot (right) 10. Switch 4 (outside right) Please note that these numbers are not meant to correspond with those given in the channel allocation table in the August issue. As I have no idea which switch you will use for what application, I cannot possibly match these numbers to the channels. They are only a guide to identifying the leads. Frequency interlock There is one correction for the August article. It stated that the charge plug must be a 2.5mm non-shorting jack. This should read “3.5mm non-shorting”. In the kit will be found two 3.5mm jack plugs. One is for the charger while the other should be fitted to the frequency key as shown in Fig.1. This plug/key combination forms the basis of the Silvertone Frequency Interlock system. Under the rules of operation for the Silvertone Keyboard frequency control system, each transmitter has its own individual key which is inserted into the Keyboard to reserve the frequency and bandwidth required for the transmitter. The only person allowed to insert or remove a key in order to reserve a frequency is the operator of the transmitter on that frequency. Thus, the logical position for the key at all other times is for it to be plugged into the transmitter, thereby rendering it inoperative. The plug/key combination performs this function. When it is inserted into With the back of the case on, the channel-setting crystal is instantly obvious. Only one transmitter may use this channel, for obvious reasons. October 1996  83 Fig.2 (left): detail of the mixing inputs and outputs. Any channel may be mixed with any other and multiple mixes are possible. Fig.3: this diagram shows how the various micro-shunts (shorting links) must be placed across TB10 if the configuration module is not used. the charge socket located on the bottom right of the transmitter control panel, the +9.6V line is open circuited, thereby rendering the transmitter inoperable even if the switch is left on. When the operator wishes to switch on, he takes his transmitter to the Keyboard and checks to see if his frequency is clear. If it is, he then removes his key from the charge socket and inserts it into the Keyboard. Thus, we now have a true frequency interlock system. If the key is in the Keyboard, the transmitter is cleared for transmission. At all other times, the key is in the charge/interlock socket on the transmitter so that the latter is inoperative. Bingo, no more inadvertent shoot downs by transmitters accidentally left on in the transmitter pound! There is an interesting sidelight to this story. When Silvertone invented and patented this system in 1969, the importers went berserk for the simple reason they would have had to pay a royalty on every transmitter sold in this country, had the system been officially adopted in Australia. They kept the system out of official use with a particularly vindictive campaign until about two years after the patent had expired. Then the very people who so vehemently campaigned against the system were the very first to start manufacturing and selling it when the coast was clear. Today the system is known as the Australian National Frequency Con84  Silicon Chip trol System and is approved for use by the MAAA at all national contests, although the frequency interlock aspect of the system is never mentioned. However, every Silvertone transmitter produced since 1969 has featured frequency interlock. Simple mixing programming This explanation will concentrate on the basic principles involved rather than covering every possible combination of mixing. Once the principles have been mastered, the rest falls into place quite easily. Four simple mixers are built into the standard Mk.22 encoder module. Two are inverting and two are non-inverting. These are located at the top righthand corner of the module and consist of a quad op-amp IC (LM324), four mix volume pots, and a double row 8-pin header plug. Fig.2 shows these controls in detail. In radio control parlance, a mixer is essentially a variable gain buffer amplifier, necessary to prevent reverse mixing when the channel inputs and outputs are connected together. Thus, a mixing amplifier is necessary for each mixing function. The input of the mixer is connected to the output of the control channel and the output of the mixer is connected to the input of the mixed channel. If you are confused by this explanation, you may like to refer back to the article on mixing in the December 1995 issue. Mixers 1 & 2 are inverting while mixers 3 & 4 are non-inverting. A non-inverting mixer will give the same direction of rotation in the mixed channel as the primary control channel. An inverting mixer will give the opposite (reverse) direction of rotation in the mixed channel to the primary. Any channel may be mixed with any other channel and multiple channel mixing is possible. Referring to Fig.3 (repeated from page 73 of the August 1996 issue), the pins numbered 1-8 carry all control input data to multiplexer IC5, including dual rate switching. The pins identified by letters are the outputs from the control stick potentiometers via the gain control pot wipers (see the circuit diagram in March 1996) and are used in certain complex mixing functions. When discussing mixing, the primary control channel from which the mix data is to be derived is considered to be the output channel. The mixer inputs and outputs may be found on the Mix Input/Output connectors TB27 and TB28, located at the extreme top right corner of the encoder module. Fig.2 shows these inputs and outputs in detail. Note that there are four pins for each mixer: an input, an output and two for the mix IN/OUT switch. Fig.4 shows the details of the mixing patch cord used to connect the mixer inputs/ outputs to the pins on TB10. One patch cord is required for each Fig 4: the mixing patch cord used to connect the mixer inputs/outputs to the pins on TB10. One patch cord is required for each mixing function. mixing function. The 2-wire, 2-pin socket connects to the appropriate mixer input/output pair with blue to mix/in and white to mix/out. The split leads go to TB10. The blue 2-pin connector is connected to the primary control (channel output) and the white 2-pin connector to the mixed channel (channel input). Two pins of the 3-pin socket on any toggle switch are connected to the switch pin pair. This provides front panel switching for mix in/out. The sense of the toggle switch (UP/OFF) is determined by which two pins are used (centre/left, centre/right). If remote switching of the mixer is not required, then the toggle switch may be replaced with a micro-shunt across the two pins. One switch or micro-shunt is required for each mixing function. Servo throw That completes the description of the basic components in the mixing circuits. Before proceeding any further, there is a very important point to bear in mind when setting up mixing functions. Each mixer input has an additive effect on servo throw and this must be taken into account when setting mix ratios. Failure to observe this may result in the servo being driven into its internal end stops with attendant gear damage. The Mk.22 has automatic compensation built in but it is still possible to drive the servo into over-travel if the mix ratios are set too high. Therefore, be sure to check the final servo travel with the full extremes of mixing applied, as servo travel varies with the brand of servo used. To illustrate the point being made in the above warning, let us examine the mixing process for a delta aircraft featuring elevons (Delta mix). Such an aircraft uses two control surfaces, one on each wing, and each control surface performs two functions: aileron and elevator control – hence the name “elevon”. Fig.5 shows the control sequence in detail. To bank such an aircraft, one control surface goes up and the other goes down, thereby imparting a rolling motion to the aircraft. To raise or lower the nose (pitch control), both control surfaces go up or down, respectively. Complications arise when one wants to bank and climb at the same time. If full throw on the aileron servo gives the desired rate of roll, what Fig. 5: the control sequence for each of a variety of movements in an aircraft fitted with elevons. Elevon controls are very complex to set up correctly. Step-by-step instructions are included in the text. happens when we then apply full up elevator to impart a climbing motion to the aircraft? If we are turning left, then some “up” mixed into the right elevon (which is down in a left roll) is easily accommodated. However, there is no more travel available in the left servo which is already full up. To apply an additional pulse width variation will only drive the servo hard into the end stops and possibly strip the gears. Therefore, the controls must be mechanically arranged so that 50% differential servo travel (one up, one down) gives the maximum rate of roll and 50% common servo travel (both up or both down) gives the maximum pitch angle. If this is done, then we may apply full pitch and roll commands simultaneously. Oddly enough, at this point only one servo actually moves and it goes to full travel. The two commands on the opposing servo cancel each other out and the servo remains in neutral. Elevon controls are very complex to set up correctly, especially when you start to consider the reflex and unequal differential angles which must be taken into account for the correct aerodynamic conditions October 1996  85 Fig. 6: this revised diagram shows the configuration module socket (TB10) in the centre of the encoder PC board. This socket was inadvertently left off the diagram published on page 73 of the August 1996 issue. required by “tail-less” aircraft. So let us move towards this complex programming task cautiously and one step at a time. Simple 2-channel mixing Such applications as Coupled Aileron/Rudder, Flap with elevator compensation and Main Rotor/Tail Rotor mixing all come under the heading of simple mixing applications and may be accomplished with the use of the simple programming patch cord and the on-board mixers. Dedicated, complex mixing utilises the configuration module and these mixing functions will form the basis of later articles. Coupled aileron/rudder with dual rate mixing In this program mode, the Aileron and Rudder controls will be coupled with an adjustable ratio of mix which will change proportionally to the dual rate ratio. To program for coupled Aileron/ Rudder, we are going to take some output from the Aileron channel and feed it into the input of the Rudder channel via one of the on-board mixers and the mix select connectors TB27 and TB28. Both the output and input programming pins are located on TB10, the configuration port connector (Fig.3). At this point, it is necessary to establish whether an inverting or non-inverting mixer is required for your application. Such details as the direction of rotation of the servos and the placement of the control linkages will all play a part here. If the complexity of working it out in your head proves too much, just whack the 2-pin connector onto a non-inverting mixer and if the rudder moves the wrong way, plonk it onto an inverting mixer; very scientific! The procedure is as follows: (1). Replace the micro-shunt from pin 2 of TB10 with the Blue socket. Next remove the micro-shunt from the rudder input on TB10 (pin 4) and replace it with the White socket. (2). Connect the 2-pin socket of the patch cord to the appropriate MIX IN­PUT/OUTPUT connectors on TB27 and TB28, with the Blue lead to “IN” and the White to “OUT”. A close-up view of the frequency interlock key. It plugs into the charging socket on the transmitter when the latter is not being used. 86  Silicon Chip (3). If remote switching of MIX IN/ OUT is required, connect two pins of the appropriate toggle switch to the “Switch” pin pair, checking the sense of operation as you go. If permanent mixing is required then place a micro-shunt across the “switch” pin pair. (4). Adjust the dual rate ratio using the Aileron channel ATV potentiometer in the usual manner and set the ratio of mix using the mix control pot associated with the mixer you have chosen. You are now programmed for Coupled Aileron/Rudder with dual rate mixing. Coupled aileron/rudder without dual rate mixing In some cases, it may be desirable to change the dual rate without changing the mix ratio. In this case, replace Steps 2 and 5 in the above with the following: (2). Connect one pin of the Blue socket to pin A on TB10, leaving the other to float free. Next, replace the micro-shunt on pin 4 with the White socket. (5). Set the ratio of mix using the appropriate mixer potentiometer. Having mastered the basics of simple mixing, and it really is simple once you get the hang of it, the same principles apply to all 24 channels in the Mk.22 transmitter. Any channel can be mixed with any other channel and even multiple channel mixing is possible using the same principles. Let us now look at the more complex task of programming for elevons. In SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ ✂ this application we begin to confront the concept of channel allocation which really is at the heart of complex mixing. Referring back to our earlier discussion on elevons and comparing it now with the channel allocation table, we find that there are no Aileron or Elevator channels, at least in the sense that we normally understand them. Instead, we are confronted with a left elevon servo and a right elevon servo, both of which respond to Aileron and Elevator commands. Where do we go from here? We still have an Aileron stick on the transmitter as well as an Elevator stick. If we allocate one to left Elevon and the other to right Elevon, I hate to think what would happen. I do not think humans would be too good at manually mixing these controls. The answer is quite simple really. We will use cross-coupled simple mixing in which we will mix channel 2 into channel 3 and channel 3 into channel 2. We will also allocate the Aileron control stick to Channel 2 and the Elevator Control stick to channel 3. Thus, the Aileron stick reverts to its normal action, as does the Elevator stick. So the programming sequence for servos of the same rotation is as follows: (1). Set both the channel 2 and channel 3 vary/normal headers to the vary position. (2). Take two patch cords and connect one to an inverting mixer and the other to a non-inverting mixer on TB27 and TB28. (3). Connect the Blue lead from the non-inverting mixer to pin E on TB10 and the Blue lead from the inverting mixer to pin A on TB10. (4). Remove the micro-shunts from TB10 pins 2 & 3 and replace them with the White socket from the non-inverting mixer to pin 2 and the White socket from the inverting mixer to pin 3. (5). Fit micro-shunts to the appropriate “switch” positions on TB27 and TB28. (6). Use both channel 2 and 3 ATV pots and both mixer volume pots to achieve perfect balance between the movement on both servos. Remember here that Aileron will send the servos in opposite directions (differential), while Elevator will send the servos in the same direction SC (common). October 1996  87